Bug 1645429 - Add tests for ReverseIterator and fix implementation of ReverseIterator::operator-. r=froydnj

Depends on D79488

Differential Revision: https://phabricator.services.mozilla.com/D79957

mfbt/ReverseIterator.h

@@ -47,7 +47,7 @@ class ReverseIterator {
 
   /* Difference operator */
   difference_type operator-(const ReverseIterator& aOther) const {
-    return -(aOther.mCurrent - mCurrent);
+    return aOther.mCurrent - mCurrent;
   }
 
   /* Increments and decrements operators */

mfbt/tests/gtest/TestReverseIterator.cpp

@@ -0,0 +1,104 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "gtest/gtest.h"
+
+#include "mozilla/ReverseIterator.h"
+
+using namespace mozilla;
+
+TEST(ReverseIterator, Const_RangeBasedFor)
+{
+  const std::vector<int> in = {1, 2, 3, 4};
+  const auto reversedRange =
+      detail::IteratorRange<ReverseIterator<std::vector<int>::const_iterator>>{
+          in.end(), in.begin()};
+
+  const std::vector<int> expected = {4, 3, 2, 1};
+  std::vector<int> out;
+  for (auto i : reversedRange) {
+    out.emplace_back(i);
+  }
+
+  EXPECT_EQ(expected, out);
+}
+
+TEST(ReverseIterator, NonConst_RangeBasedFor)
+{
+  std::vector<int> in = {1, 2, 3, 4};
+  auto reversedRange =
+      detail::IteratorRange<ReverseIterator<std::vector<int>::iterator>>{
+          in.end(), in.begin()};
+
+  const std::vector<int> expected = {-1, -2, -3, -4};
+  for (auto& i : reversedRange) {
+    i = -i;
+  }
+
+  EXPECT_EQ(expected, in);
+}
+
+TEST(ReverseIterator, Difference)
+{
+  const std::vector<int> in = {1, 2, 3, 4};
+  using reverse_iterator = ReverseIterator<std::vector<int>::const_iterator>;
+
+  reverse_iterator rbegin = reverse_iterator{in.end()},
+                   rend = reverse_iterator{in.begin()};
+  EXPECT_EQ(4, rend - rbegin);
+  EXPECT_EQ(0, rend - rend);
+  EXPECT_EQ(0, rbegin - rbegin);
+
+  --rend;
+  EXPECT_EQ(3, rend - rbegin);
+
+  ++rbegin;
+  EXPECT_EQ(2, rend - rbegin);
+
+  rend--;
+  EXPECT_EQ(1, rend - rbegin);
+
+  rbegin++;
+  EXPECT_EQ(0, rend - rbegin);
+}
+
+TEST(ReverseIterator, Comparison)
+{
+  const std::vector<int> in = {1, 2, 3, 4};
+  using reverse_iterator = ReverseIterator<std::vector<int>::const_iterator>;
+
+  reverse_iterator rbegin = reverse_iterator{in.end()},
+                   rend = reverse_iterator{in.begin()};
+  EXPECT_TRUE(rbegin < rend);
+  EXPECT_FALSE(rend < rbegin);
+  EXPECT_FALSE(rend < rend);
+  EXPECT_FALSE(rbegin < rbegin);
+
+  EXPECT_TRUE(rend > rbegin);
+  EXPECT_FALSE(rbegin > rend);
+  EXPECT_FALSE(rend > rend);
+  EXPECT_FALSE(rbegin > rbegin);
+
+  EXPECT_TRUE(rbegin <= rend);
+  EXPECT_FALSE(rend <= rbegin);
+  EXPECT_TRUE(rend <= rend);
+  EXPECT_TRUE(rbegin <= rbegin);
+
+  EXPECT_TRUE(rend >= rbegin);
+  EXPECT_FALSE(rbegin >= rend);
+  EXPECT_TRUE(rend >= rend);
+  EXPECT_TRUE(rbegin >= rbegin);
+
+  EXPECT_FALSE(rend == rbegin);
+  EXPECT_FALSE(rbegin == rend);
+  EXPECT_TRUE(rend == rend);
+  EXPECT_TRUE(rbegin == rbegin);
+
+  EXPECT_TRUE(rend != rbegin);
+  EXPECT_TRUE(rbegin != rend);
+  EXPECT_FALSE(rend != rend);
+  EXPECT_FALSE(rbegin != rbegin);
+}

mfbt/tests/gtest/moz.build

@@ -7,6 +7,7 @@
 UNIFIED_SOURCES += [
     'TestBuffer.cpp',
     'TestLinkedList.cpp',
+    'TestReverseIterator.cpp',
     'TestSpan.cpp',
 ]